That hole was only used on the late 32 and than again on the late 33 and early 34 firewalls. They discontinued that hole for various reasons as explained in the book by Rector C Fiellds that was published in 1939. A copy of this book is hard to find and they demand big money. The book was reprinted in 1941 and all of the originals were thrown away which created a big demand for the second printing. You should pic up copy of this book and you will get less information about this hole than you have from this quick reply.
I other words I do not have a clue but I just cleaned my keyboard and wanted to see if it still works.
This quick reply should prevent you for thanking people in advance. Just kidding.